1. Field of the Invention
The present invention relates to a photodetecting device for detecting radiation of a plurality of wavelengths, more specifically, to a multi-color infrared focal plane array (IRFPA) using an absorption of infrared radiation by a quantum level of a quantum well structure or a quantum dot structure.
2. Description of the Related Art
For infrared imaging in an 8-12 xcexcm wavelength range, quantum-well infrared photodetectors (QWIPs) using quantum well structures of compound semiconductors are used. The QWIPs have multi-quantum well (MQW) structure, which has quantum well structures stacked repeatedly by a plurality of times, and are infrared radiation detectors using electric conductivity changes due to contribution of electrons in the quantum wells excited by application of infrared radiation. As one of such infrared radiation detectors is known the infrared radiation detector described in the specification of Japanese Patent Laid-Open Publication No. 241064/1990, which has not a plurality of detecting elements but a single detecting element.
Recently a multi-color infrared radiation detector of multi-quantum well structures having different quantum levels for detecting infrared radiation of a plurality of wavelengths is proposed. One picture element of such infrared radiation detector will be explained with reference to FIG. 11.
A first multi-quantum well structure 102 and a second quantum well structure 104 are laid the one on the other on a semiconductor substrate 100. The first multi-quantum well structure 102 and the second multi-quantum well structure 104 are different from each other in the thickness of the quantum well layer and the composition ratio thereof, whereby both structures have quantum levels different from each other. Accordingly, a wavelength of infrared radiation absorbed by the first multi-quantum well structure 102 is different from that absorbed by the second multi-quantum well structure 104.
A first electrode 110 is formed on the underside of the first multi-quantum well structure 102. A second electrode 112 is formed on the upper side of the first multi-quantum well structure 102. A third electrode 114 is formed on the upper side of the second quantum well structure 104. An electric conductivity between the first electrode 110 and the second electrode 112, and an electric conductivity between the second electrode 112 and the third electrode 114 are measured to thereby separately detect infrared radiation of different wavelengths.
When a plurality of such picture elements are arranged in a matrix to form an IRFPA, the structure shown in FIG. 11 requires the three electrodes 110, 112, 114 for each picture element. The electrodes 110, 112, 114 occupy an accordingly large area per one picture element, with a result of low detection sensitivity.
In the structure shown in FIG. 11, the second electrode 112 could be the common electrode for each picture element, but the structure makes it impossible. This is because the first electrode 110 and the third electrode 114 of one picture element must be separated from those of another picture element. Accordingly, the structure shown in FIG. 11 does not allow the electrode to be commonly used to increase the detection area for higher detection sensitivity.
An object of the present invention is to provide a photodetecting device having area required for electrode decreased for higher detection sensitivity.
The above-described object is achieved by a photodetecting device comprising: a first quantum well structure including a first quantum well layer doped with an impurity, and having a first quantum level absorbing a radiation of a first wavelength; and a second quantum well structure laid on the first quantum well structure, including a second quantum well layer non-doped with an impurity, and having a second quantum level absorbing a radiation of a second wavelength which is different from the first wavelength.
The above-described object is also achieved by a photodetecting device comprising: a first quantum well structure including a first quantum well layer non-doped with an impurity, and having a first quantum level absorbing a radiation of a first wavelength; and a second quantum well structure laid on the first quantum well structure, including a second quantum well layer non-doped with an impurity, and having a second quantum level absorbing a radiation of a second wavelength which is different from the first wavelength.
The above-described object is also achieved by a photodetecting device comprising: a first quantum dot structure including a first quantum dot doped with an impurity, and having a first quantum level absorbing a radiation of a first wavelength; and a second quantum dot structure laid on the first quantum dot structure, including a second quantum dot non-doped with an impurity, and having a second quantum level absorbing a radiation of a second wavelength which is different from the first wavelength.
The above-described object is also achieved by a photodetecting device comprising: a first quantum dot structure including a first quantum dot non-doped with an impurity, and having a first quantum level absorbing a radiation of a first wavelength; and a second quantum dot structure laid on the first quantum dot structure, including a second quantum dot non-doped with an impurity, and having a second quantum level absorbing a radiation of a second wavelength which is different from the first wavelength.
The above-described object is also achieved by a photodetecting apparatus comprising: the above-described photodetecting device; and a radiation source for radiating a pump radiation of the second wavelength to the second quantum well structure.
The above-described object is also achieved by a photodetecting apparatus comprising: the above-described photodetecting device; a first radiation source for radiating a first pump radiation of the first wavelength to the first quantum dot structure; and a second radiation source for radiating a second pump radiation of the second wavelength to the second quantum dot structure.
The above-described object is also achieved by a method of controlling the above-described photodetecting device, comprising the steps of: applying a pump radiation of a wavelength generating carriers in the second quantum level; and detecting radiation of the second wavelength in synchronization with the application of the pump radiation.
The above-described object is also achieved by a method of controlling the above-described photodetecting device, comprising the steps of: applying a first pump radiation of a wavelength generating carriers in the first quantum level; and a second pump radiation of a wavelength generating carriers: in the second quantum level; and detecting a radiation of the first wavelength in synchronization with the application of the first pump radiation, and detecting a radiation of the second wavelength in synchronization with the application of the second pump radiation.
As described above, according to the present invention, the first quantum well structure including the first quantum well layer doped with an impurity and having a first quantum level absorbing a first wavelength, and the second quantum well structure including the second quantum layer non-doped with an impurity and having a second quantum level absorbing a second wavelength, which are stacked one on the other, whereby a required electrode area can be smaller to thereby obtain higher detection sensitivity.